1. Field
The present invention relates to devices for charging batteries and to batteries which can be charged with a charging device.
2. Description of Prior Art
Cordless medical handheld devices or handpieces having an internal power source in the form of batteries are becoming increasingly popular because of their ease of handling in comparison with handheld devices connected by a power cable to an external power source. Because of the different requirements, e.g., with respect to the power, design type or size of such cordless handheld devices, there is also a constantly proliferating number of batteries or types of batteries having different storage capacities, power supply, design, charging requirements, etc. To avoid requiring a separate charger for each type of battery, the charger units are designed so that different batteries may be connected to them. This means that the terminal or contact device of the charger is designed so that batteries of different designs or sizes can be connected to the chargers and/or that a charging circuit is provided that adapts the charging requirements to the particular connected battery, i.e., supplying it with the required power supply voltage or amperage or selecting the suitable charging method.
If a charger can adapt the charging current or the charging method to the connected battery, then before the start of the charging operation, it is necessary to determine the type of battery by means of an identification device and to select the respective charging method and/or the proper charging current parameters. Various approaches are known in this regard from the state of the art, e.g., mechanical switches, contacts of different lengths on the batteries, e.g., as disclosed in U.S. Pat. No. 5,187,422, or resistance measurements, with each type of battery being provided with a recognition resistor. By determining the resistance value, it is possible to recognize the different types of batteries. All these identification devices have disadvantages, however; in particular due to the repeated use there may be changes in the mechanical components, so that invalid contact resistances occur in the resistance measurement, for example, and therefore the type of battery is not recognized at all or is identified incorrectly.
It would be advantageous to create a device for charging batteries of medical equipment using an alternative means of recognizing the batteries that is inexpensive, reliable, even after repeated uses, and easy to manufacture and to create a corresponding battery.